Optative.—The optative adds -ι_- or -ιη- to the tense-stem ending in -θε- or -ε-, and contracts. In the singular -ιη- is regular; in the dual and plural -ι_- is generally preferred. Thus λυθείην from λυθε-ίη-ν, φανείην from φανε-ίη-ν,
λυθεῖτον from λυθέ-ι_-τον, φανεῖτον from φανέ-ι_-τον, λυθεῖμεν from λυθέ-ι_-μεν, φανεῖεν from φανέ-ιε-ν. The inflection is like that of the present optative of a μι-verb.
a. -είημεν is used only in prose (but Plato and Isocrates have also -εῖμεν). -είητε is almost always found in the Mss. of prose writers; -εῖτε occurs only in poetry (except from μι-verbs). -εῖεν is more common in prose than -είησαν.
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].